Current converting device



May 2, l 933.

R. D. FAY

CURRENT CONVERT ING DEVICE Filed Dec. 25, 192'! 11v VENTOR. Rab/2 am D. Fay

W WW

ATTORNEY.

Patented May 2, 19 33 UNITED STATES PATENT RICHARD DUDLEY FAY, OF CAMBRIDGE, lvIASSACHUE-ETTS, ASSIGNOR TO SUBMARINE SIGNAL CORPORATION, OF BOSTON, MASSACHUSETTS, A CORPORATION OF DELA- WARE CURRENT OONV ERTIN G DEVICE Application filed December 23, 1927.

The present invention relates to the conversion of direct current into alternating current and also alternating currents of one voltage and frequency to currents of a difierent 5 voltage and frequency, and more particularly in such a manner as to avoid means for breaking an electrical contact, such as a me chanical interrupter or commutator.

In the prior art, attempts have been made to convert direct current into alternating cur rentby commutator and interruptor devices, but such devices have not proved successful in many cases, even where arcing between contacts has been reduced to a minimum by various known methods, because the wear on the mechanical elements changes conditions in such a manner that either the contact resistance is altered or arcing finally occurs or some other condition arises which makes the device inefficient or inoperative.

While condensers across the contacts tend to prevent an arc across the latter, it is, how ever, Very difficult, if not impossible, to remove entirely the arcing across contacts as they are opened, so that continued operation of contact devices usually produces pitting or wearing of one or both contacts and impairment of the efficient operation of the circuit.

For currents of low frequencies, construction of contact and commutator devices for changing direct current into alternating current is not difficult, since commutators and contacts move and vibrate respectively quite slowly for low frequencies. But when it is desired to produce frequencies which correspond in sound frequencies to those in and above the audible range, the problem becomes more difficult and increases in difliculty as it is attempted to produce higher frequencies. In the higher frequencies, suflicient amplitude cannot be obtained with contact devices such as tuning forks and interruptors; and commutators produce arcing on account of the high potential existing between segments and the metallic dust particles which settle over Serial No. 242,253.

alternating current from direct current new methods are necessary.

in the present invention, recognizing these difficulties, I avoid the use of contact and commutator devices and cause a current to flow and cease abruptly by the use of gaseous tubes in which a trigger electrode or other suitable means supplied with a sufficient potential causes the current to flow from one electrode to another in the tube, and in. which the current is suddenly cut off by the back electromotive force of an inductance or some suitable voltage supplied in the opposite direction to that which initially set up the current. By the use of such a gaseous tube, which may contain neon gas and three electrodes, an anode, a grid and a cathode, I am able to commence the flow of current in a given direction and then abruptly cut it off without necessitating the interruption of currents by contact devices such as commutators or vibrating interruptors.

l/Vithout further preliminary explanations the invention will be described. with reference to the drawing, which shows diagrammatically the electrical circuit and apparatus.

In the figure the terminals at the left marked 1 and 2 connect respectively to the negative and positive of the direct current source. In series with the negative side of the line, as shown in this figure, and in parallel with each other are the gaseous conducting tubes 3 and 4. These tubes, according to the invention, could be placed in the positive side of the line without materially affecting the operation. Each tube has an anode 5, a cathode or plate 6 as it will be designated in the present description, which it will be noted is not the term used in description of thermionic tubes for the same element, and a grid 7. The negative side of the line connects directly to the cathodes 6 of the tubes 3 and 4, the anodes of which are connected to each other through the primary of a transformer 8, the middle point of which is connected by the lead 18 to the positive side 2 of the direct current line. The secondary of the transformer 8 connects to the power output side marked A. C.

Normally the gaseous tubes 3 and 4 are non-conducting until ionization of the gas within the tube takes place and forms a conducting path for the current. There is, however, a critical potential which, if applied, will cause the ionization to take place, thus lowering the resistance of the path allow ing conduction. In the present application, this ionization is produced by means of a third electrode 7, called a grid electrode, which is given a sufficiently high potential to ionize the gas between the cathode and the grid and commence conduction between the cathode and the anode, and subsequently a sufiiciently high relative potential to stop conduction.

This potential for starting and stopping the operation is applied to the grids of the tubes by means of a thermionic circuit made to oscillate at the desired frequency by known means as for instance the inductance and the variable capacity 31.

Since the thermionic circuit is made to oscillate, the current in the plate circuit of the tube oscillates. By connecting the point 41 in this circuit, which is between the inductance 42 and the capacity 43, to the negative side of the line, the cathode 6 will have the potential of this point. Since the voltage across the inductance 42 is 180 out of phase with that across the capacity 43, when the potential on one grid is positive that on the other grid will be negative. If, now, the positive potential is sufficient to start conduction and the negative potential suflicient to stop conduction, the arrangement of the figure accomplishes the result without the use of commutators at all. By proper choice of inductances and capacities, this can easily be accomplished.

During one half cycle, therefore, a positive potential is applied to the grid of the tube 3 and during the next half cycle a negative potential, cutting off the conduction which has been commenced by the application of the positive potential. While the positive potential has been applied to the grid of tube 3 a negative potential is being applied to the grid of tube 4, cutting off the conduction which had previously been commenced, by the application of a positive potential to the grid of the tube 4. Current will therefore alternately flow through each tube and produce currents in the primary of transformer 8 flowing alternately through the up r half of the primary downward to lead 18 and then through the lower half upward to lead 18, thus producing alternating current in the load circuit. 46 is a resistance used to limit the current in the auxiliary circuit.

This system, while partly useful for transforming alternating currents of low frequency and voltage to high frequency and high voltage, may conveniently be used for transforming alternating currents of one frequency and voltage to that of another frequency and voltage, whether the latter be higher or lower than the former.

Having now described my invention, I claim:

A system for converting direct current to alternating current comprising two gaseous tubes, each having a cathode, an anode and a grid, a source of direct current, one side of which is connected to said cathodes, a transformer having a primary and a secondary, the midpoint of said primary being connected to the other side of said direct current source, and the extremities of said primary being connected to said anodes, a tunable oscillatory thermionic vacuum tube ci 'cuit having connected across its output an inductance and a capacity in series, the point between said inductance and said capacity being connected to said cathodes, the second terminal of said inductance being connected to the grid of one gaseous tube, and the second terminal of said capacity being connected to the grid of the second gaseous tube, whereby current will flow alternately in the two gaseous tubes and an alternating current will be set up in the secondary of said transformer.

In testimony whereof I afiix my signature.

RICHARD D. FAY. 

